1. Field of the Invention
This invention relates to an automatic material feeding system in a press, and more particularly to a roll feeder adopting a barrel cam drive system suited for use as an automatic material feeding device in a high-speed press.
2. Prior Art
As is well known, a roll feeder comprises essentially a driving feed roll and a driven feed roll disposed in opposition and pressed contact with said driving feed roll so as to be driven thereby, and the driving roll is turned intermittently while maintaining a constant timed relation with reciprocation of the cope or forming member of the press, thereby to effect power feed of the work held and worked between both rolls. The most important requisite in such power feed is to minimize the error between the schemed feed distance and the actual feed distance, that is to say, to maintain the set feed accuracy constantly. Such maintenance of feed accuracy won't be ensured unless smooth and accurate transmission of motion from the press body to the main driving feed roll is provided. In other words, it is essential that the motion transmission mechanism between the crank shaft which reciprocates the press ram and the roll feeder be designed and worked such that no excess or undue stress or force will be built up in the structural mechanisms. In the conventional roll feeder devices, a crank motion mechanism has been employed as the motion transmission mechanism. For instance, an eccentric disc is mounted at an end of the crank shaft designed to effect up and down movement of the press ram, while a one-way ratchet mechanism is operatively associated with the driving feed roll of the roll feeder, with the eccentric shaft of said eccentric disc being coupled to said one-way ratchet mechanism by a connecting rod, so that one rotation of the crank shaft will provide one reciprocation of the press ram while letting the driving feed roll turn intermittently through said connecting rod and one-way ratchet mechanism during each rotation of the crank shaft, thereby to effect automatic intermittent feed of the work.
In this case, it is to be noted that transmission of motion from the crank shaft of the press to the driving feed roll of the roll feeder has a nature that it tends to constantly change the rotating speed of the driving feed roll during the entire process of rotation notwithstanding the fact that the crank shaft of the press rotates at constant speed. Further, since the time of motion of the press ram and the time of turn of the driving feed roll, have therebetween a difference of 90.degree. in terms of the angle of turn of the crank shaft, when the press ram is at its upper dead point the driving feed roll is turned at the highest speed in the entire process of rotation at the time when the press ram begins its descent from the upper dead point. Also, when the angle of turn of the crank shaft reaches 90.degree., that is, when the press ram just begins its stroke, the eccentric disc and the connecting rod will now have the angular difference of 180.degree., so that although the driving feed roll ceases to rotate, acceleration of the driving feed roll at that time is maximized.
In such type of motion transmission mechanism, it is hard to maintain constant feed accuracy, and it is even more difficult to ensure constant feed accuracy while maintaining high-speed feed of the work. This is mostly due to the following reason. That is, if the rotating speed of the driving feed roll is changed during its process of rotation, it can cause itself inaccurate transmission of the friction-based motion from the driving and driven feed rolls to the material to be fed, and particularly when the driving and driven feed rolls are stopped, the maximum acceleration produced at that moment gives a large inertia to both said driving and driven feed rolls and the material to be fed, and this could cause sliding between them and thus badly affect feed accuracy, resulting in producing an error between the schemed feed distance and the actual feed distance to make it impossible to maintain the constant feed accuracy. This is witnessed particularly when the press speed is increased, that is, when the work is fed at high speed for effecting high-speed work.
Thus, the conventional roll feeder employing such crank motion mechanism in the motion transmission mechanism can not be safely adapted to an automatic material feeding system for a press which is basically designed for high-speed works. Such low feed accuracy leads immediately to reduced utilization rate of the material. Further, in the systems employing such a motion transmission mechanism, there are involved many joints used for connecting. For instance, the eccentric disc and connecting rod, the connecting rod and one-way ratchet mechanism, etc., and such joints have a possibility to become loose in the course of use and looseness of such joints causes even lower feed accuracy. Also, a large number of such joints gives a greater opportunity of causing backlash and consequent generation of noise and shaking, resulting generally in reduced working efficiency.